U.S. patent number 9,905,420 [Application Number 14/956,115] was granted by the patent office on 2018-02-27 for methods of forming silicon germanium tin films and structures and devices including the films.
This patent grant is currently assigned to ASM IP Holding B.V.. The grantee listed for this patent is ASM IP Holding B.V.. Invention is credited to Joe Margetis, John Tolle.
United States Patent |
9,905,420 |
Margetis , et al. |
February 27, 2018 |
Methods of forming silicon germanium tin films and structures and
devices including the films
Abstract
Methods of forming silicon germanium tin
(Si.sub.xGe.sub.1-xSn.sub.y) films are disclosed. Exemplary methods
include growing films including silicon, germanium and tin in an
epitaxial chemical vapor deposition reactor. Exemplary methods are
suitable for high volume manufacturing. Also disclosed are
structures and devices including silicon germanium tin films.
Inventors: |
Margetis; Joe (Gilbert, AZ),
Tolle; John (Gilbert, AZ) |
Applicant: |
Name |
City |
State |
Country |
Type |
ASM IP Holding B.V. |
Almere |
N/A |
NL |
|
|
Assignee: |
ASM IP Holding B.V. (AP Almere,
NL)
|
Family
ID: |
58777714 |
Appl.
No.: |
14/956,115 |
Filed: |
December 1, 2015 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170154770 A1 |
Jun 1, 2017 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
21/02532 (20130101); H01L 21/02452 (20130101); H01L
29/161 (20130101); H01L 21/02505 (20130101); H01L
21/0262 (20130101); H01L 21/0245 (20130101); H01L
21/02535 (20130101); H01L 21/02636 (20130101); H01L
29/165 (20130101) |
Current International
Class: |
H01L
21/20 (20060101); H01L 21/36 (20060101); H01L
21/02 (20060101); H01L 29/161 (20060101); H01L
29/165 (20060101) |
Field of
Search: |
;438/478,752,753,933,75
;257/190,183 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Mosleh et al., Enhancement of Material Quality of (Si)GeSn Films
Grown by SnCL4 Precursor, Oct. 2015, ECS Transactions, 69 (5), p.
279-285. cited by examiner.
|
Primary Examiner: Malsawma; Lex
Assistant Examiner: Ojeh; Nduka
Attorney, Agent or Firm: Snell & Wilmer L.L.P.
Claims
What is claimed is:
1. A method of forming a Si.sub.xGe.sub.1-xSn.sub.y layer on a
substrate, the method comprising the steps of: providing a reactor
having a reaction space; providing a substrate within the reaction
space; providing silane coupled to the reaction space; providing a
germanium precursor coupled to the reaction space; providing a tin
precursor source coupled to the reaction space; and epitaxially
forming a layer of Si.sub.xGe.sub.1-xSn.sub.y on a surface of the
substrate, wherein a pressure in the reaction space is between
about 500 Torr and about 760 Torr and a temperature in the reaction
space is between about 200.degree. C. and about 500.degree. C.,
wherein a ratio of a flowrate of the silane to a flowrate of the
tin precursor is between about 2 to about 15, and wherein the
Si.sub.xGe.sub.1-xSn.sub.y layer comprises about 2 at % to about 15
at % tin, and about 55 at % to about 65 at % germanium.
2. The method of forming a Si.sub.xGe.sub.1-xSn.sub.y layer
according to claim 1, wherein the germanium precursor comprises
germane.
3. The method of forming a Si.sub.xGe.sub.1-xSn.sub.y layer
according to claim 1, wherein, during the step of epitaxially
forming a layer of Si.sub.xGe.sub.1-xSn.sub.y on a surface of the
substrate, an operating pressure of the reaction space is between
about 600 Torr and about 760 Torr.
4. The method of forming a Si.sub.xGe.sub.1-xSn.sub.y layer
according to claim 1, wherein the layer of
Si.sub.xGe.sub.1-xSn.sub.y comprises about 3 at % to about 12 at %
tin.
5. The method of forming a Si.sub.xGe.sub.1-xSn.sub.y layer
according to claim 1, wherein the layer of
Si.sub.xGe.sub.1-xSn.sub.y comprises greater than 0 to about 30 at
% silicon.
6. The method of forming a Si.sub.xGe.sub.1-xSn.sub.y layer
according to claim 1, wherein the layer of
Si.sub.xGe.sub.1-xSn.sub.y comprises about 1 at % to about 2 at %
carbon.
7. The method of forming a Si.sub.xGe.sub.1-xSn.sub.y layer
according to claim 1, wherein, during the step of epitaxially
forming a layer of Si.sub.xGe.sub.1-xSn.sub.y on a surface of the
substrate, a ratio of the silane to the germanium precursor
provided to the reaction space is about 2 to about 15.
8. The method of forming a Si.sub.xGe.sub.1-xSn.sub.y layer
according to claim 1, wherein, during the step of epitaxially
forming a layer of Si.sub.xGe.sub.1-xSn.sub.y on a surface of the
substrate, a ratio of the silane to the germanium precursor
provided to the reaction space is about 3 to about 12.
9. The method of forming a Si.sub.xGe.sub.1-xSn.sub.y layer
according to claim 1, wherein, during the step of epitaxially
forming a layer of Si.sub.xGe.sub.1-xSn.sub.y on a surface of the
substrate, an operating temperature within the reaction space is
about 275.degree. C. to about 475.degree. C.
10. The method of forming a Si.sub.xGe.sub.1-xSn.sub.y layer
according to claim 1, wherein the step of providing a tin precursor
comprises providing a tin source selected from one or more of the
group of SnCl.sub.4, SnD.sub.4, and a methyl and/or halide
substituted stannate.
11. The method of forming a Si.sub.xGe.sub.1-xSn.sub.y layer
according to claim 1, wherein the step of epitaxially forming a
layer of Si.sub.xGe.sub.1-xSn.sub.y on a surface of the substrate
comprises growing a crystalline layer comprising about 4 at % to
about 5 at % carbon.
12. The method of forming a Si.sub.xGe.sub.1-xSn.sub.y layer
according to claim 1, wherein the step of epitaxially forming a
layer of Si.sub.xGe.sub.1-xSn.sub.y on a surface of the substrate
comprises growing a crystalline layer comprising 1 at % to about 30
at % silicon.
13. A method of forming a structure comprising a
Si.sub.xGe.sub.1-xSn.sub.y layer, the method comprising the steps
of: providing a cross-flow reactor comprising a reaction space;
providing a substrate within the reaction space; and forming a
crystalline layer comprising Si.sub.xGe.sub.1-xSn.sub.y on a
surface of the substrate using silane and germane, wherein, during
the step of forming, a pressure in the reaction space is between
about 500 Torr and about 760 Torr and a temperature is between
about 200.degree. C. and about 500.degree. C., wherein, during the
step of forming, a ratio of the silane to the germane provided to
the reaction space is about 2 to about 15, wherein a ratio of a
flowrate of the silane to a flowrate of a tin precursor is between
about 2 to about 15, and wherein the Si.sub.xGe.sub.1-xSn.sub.y
layer comprises about 2 at % to about 15 at % tin, and about 60 at
% to about 70 at % germanium.
14. The method of forming a structure comprising a
Si.sub.xGe.sub.1-xSn.sub.y layer of claim 13, wherein the substrate
comprises a layer comprising germanium overlying silicon.
15. The method of forming a structure comprising a
Si.sub.xGe.sub.1-xSn.sub.y layer of claim 13, wherein the layer
comprising Si.sub.xGe.sub.1-xSn.sub.y comprises about 3 from
greater than 0 at % tin to about 12 at % tin.
16. The method of forming a structure comprising a
Si.sub.xGe.sub.1-xSn.sub.y layer of claim 13, wherein the layer
comprising Si.sub.xGe.sub.1-xSn.sub.y comprises from greater than 0
at % silicon to about 30 at % silicon.
17. The method of forming a structure comprising a
Si.sub.xGe.sub.1-xSn.sub.y layer of claim 13, wherein the layer
comprising Si.sub.xGe.sub.1-xSn.sub.y comprises about 2 at %
germanium to about 3 at % carbon.
18. The method of forming a structure comprising a
Si.sub.xGe.sub.1-xSn.sub.y layer of claim 13, further comprising
the steps of: forming an insulating layer overlying the substrate;
forming a via within the insulating layer, and selectively forming
the layer comprising Si.sub.xGe.sub.1-xSn.sub.y within the via.
19. A structure comprising a crystalline layer of
Si.sub.xGe.sub.1-xSn.sub.y formed according to the method of claim
13.
20. The structure of claim 19, wherein the structure comprises a
layer comprising germanium overlying the crystalline layer of
Si.sub.xGe.sub.1-xSn.sub.y.
Description
FIELD OF INVENTION
The present disclosure generally relates to techniques for forming
layers including silicon germanium tin and to structures and
devices including such layers. More particularly, various
embodiments of the disclosure relate to methods of forming silicon
germanium tin layers using germane and/or silane, to methods of
forming structures and devices including such layers, to systems
for forming the layers and structures, and to structures and
devices including the layers.
BACKGROUND OF THE DISCLOSURE
Various electronic devices, such as semiconductor devices, and
photonic devices, such as lasers and solar devices, include or may
desirably include silicon germanium tin
(Si.sub.xGe.sub.1-xSn.sub.y) layers. For example,
Si.sub.xGe.sub.1-xSn.sub.y layers can be used to form direct band
gap devices, quantum well structures, and/or may be used to provide
strain in, for example, an adjacent germanium layer to increase
carrier mobility in the germanium layer. Si.sub.xGe.sub.1-xSn.sub.y
layers can also be used to form tunable band gap devices as well as
optical devices having tunable optical properties. To obtain the
desired device properties, the Si.sub.xGe.sub.1-xSn.sub.y layers
generally have a crystalline structure, which generally follows the
crystalline structure of an underlying layer, such as a buffer
layer.
Si.sub.xGe.sub.1-xSn.sub.y layers can be deposited or grown using a
variety of techniques. For example, vacuum processes, including
molecular beam epitaxy and ultra-high vacuum chemical vapor
deposition, have been used to form Si.sub.xGe.sub.1-xSn.sub.y
films. Unfortunately, such techniques are slow, expensive, and thus
generally not well suited for high-volume manufacturing.
The germanium precursor for such processes typically includes
digermane (Ge.sub.2H.sub.6) or trigermane (Ge.sub.3H.sub.8). When
the film includes silicon, the silicon precursor typically includes
a disilane (Si.sub.2H.sub.6), trisilane (Si.sub.3H.sub.8), or other
higher order silane compounds, or hetero-nuclear Si--Ge compounds
with the general formula of (H.sub.3Ge)xSiH.sub.4-x (x=1-4),
(H.sub.3Si)xGeH.sub.4-x (x=1-4).
Although such processes generally work to deposit or grow
crystalline Si.sub.xGe.sub.1-xSn.sub.y layers, use of digermane,
trigermane, or higher order germane precursors and/or disilane or
trisilane, is problematic in several respects. For example,
formation of films or layers including Si.sub.xGe.sub.1-xSn.sub.y
using digermane or higher order germane precursors, such as
trigermane, is not selective when certain carrier gasses (e.g.,
hydrogen) and/or dopants (e.g., p-type dopants) are used with the
precursor. Also, digermane is relatively unstable (explosive) in
concentrated form; as a result, an amount of the precursor
contained in a vessel may be limited, typically to less than 154
grams, which, in turn, causes throughput of processes using such a
precursor to be relatively low. In addition, digermane and higher
order germanes are relatively expensive. Similarly, higher order
silanes are relatively expensive and can result in relatively slow
growth rates. Accordingly, improved processes for forming
Si.sub.xGe.sub.1-xSn.sub.y are desired. Further, improved methods
suitable for high-volume manufacturing of structures and devices
including a layer of Si.sub.xGe.sub.1-xSn.sub.y are desired.
SUMMARY OF THE DISCLOSURE
Various embodiments of the present disclosure relate to methods of
forming Si.sub.xGe.sub.1-xSn.sub.y films, to structures and devices
including Si.sub.xGe.sub.1-xSn.sub.y films, and to systems for
forming the Si.sub.xGe.sub.1-xSn.sub.y films. The methods described
herein can be used to form Si.sub.xGe.sub.1-xSn.sub.y films
suitable for a variety of applications, including, for example,
stressor films in semiconductor devices and tunable bandgap layers
in photonic devices. While the ways in which various embodiments of
the disclosure address the drawbacks of the prior art methods,
films, structures, devices, and systems are discussed in more
detail below, in general, the disclosure provides methods of
forming Si.sub.xGe.sub.1-xSn.sub.y using silane and/or germane as
precursors. Exemplary methods can be used to form films,
structures, and/or devices including Si.sub.xGe.sub.1-xSn.sub.y in
a cost efficient manner and/or can be used to form such films,
structures and/or devices in a time efficient manner. Various
methods described herein are particularly well suited for use in
high volume manufacturing of structures and devices including
Si.sub.xGe.sub.1-xSn.sub.y films.
As used herein, Si.sub.xGe.sub.1-xSn.sub.y films (also referred to
herein as layers) are layers that can include the elements silicon,
germanium, and tin. In accordance with various embodiments of the
disclosure, the Si.sub.xGe.sub.1-xSn.sub.y films are crystalline
and are epitaxially formed overlying a crystalline substrate or
layer. The films can be in the form of an alloy. Exemplary
Si.sub.xGe.sub.1-xSn.sub.y films include from 0 or greater than 0
at % to about 15 at % or about 2 at % to about 15 at % tin, from 0
or greater than 0 at % to about 30 at % or about 1 at % to about 30
at % silicon, or about 55 at % to about 65 at % or about 75 at % to
about 95 at % germanium. The layers can include additional
elements, such as carbon (e.g., GeSnSiC alloys) and/or other
elements, such as phosphorous, boron, or other elements commonly
used as dopants, and/or trace amount of other elements.
In accordance with some exemplary embodiments of the disclosure,
methods of forming a Si.sub.xGe Sn.sub.Y layer on a substrate
include the steps providing a reactor having a reaction space,
providing a substrate within the reaction space, providing silane
coupled to the reaction space, providing a germanium precursor
(e.g., germane) coupled to the reaction space, providing a tin
precursor source coupled to the reaction space, and epitaxially
forming a layer of Si.sub.xGe.sub.1-xSn.sub.y on a surface of the
substrate. One or more of the precursors can be mixed at or near an
inlet of the reaction chamber--e.g., at an inlet or injection
manifold of the reactor. In accordance with further aspects, a
cross-flow reactor is used to form the Si.sub.xGe.sub.1-xSn.sub.y
layer(s). In accordance with yet further aspects, a ratio of
flowrate of silane to the tin precursor (not including carrier
gasses) ranges from about 2 to about 5, or about 2 to about 10, or
about 2 to about 15. Exemplary methods can further include
providing additional precursors, such as carbon precursors and/or
dopant precursors, to the reaction space; such additional
precursor(s) can be mixed with one or more of the other precursors
at or near the inlet of the reaction chamber and/or further
upstream of the reactor.
Other exemplary methods of forming a Si.sub.xGe.sub.1-xSn.sub.y
layer on a substrate include the steps providing a reactor (e.g., a
cross-flow reactor) having a reaction space, providing a substrate
within the reaction space, providing a silicon source (e.g.,
silane) coupled to the reaction space, providing germane coupled to
the reaction space, providing a tin precursor source coupled to the
reaction space, and epitaxially forming a layer of
Si.sub.xGe.sub.1-xSn.sub.y on a surface of the substrate. A ratio
of flowrate of silane to the tin precursor ranges from about 2 to
about 15 or other silane:tin precursor ratios as set forth herein.
Exemplary methods can further include providing additional
precursors, such as carbon precursors and/or dopant precursors, to
the reaction space; such additional precursor(s) can be mixed with
one or more of the other precursors at or near the inlet or further
upstream of the reaction chamber.
A reaction space temperature for methods described herein can range
from about 200.degree. C. to about 500.degree. C., about
275.degree. C. to about 475.degree. C., or about 300.degree. C. to
about 420.degree. C. Exemplary reaction chamber pressures during
this step range from about 500 Torr to about 760 Torr, about 600
Torr to about 760 Torr, or about 700 Torr to about 760 Torr. The
relatively low temperatures and/or relatively high pressures allow
for low throughput times associated with manufacturing structures
and devices comprising one or more Si.sub.xGe.sub.1-xSn.sub.y
layers formed as described herein.
In accordance with exemplary aspects of various embodiments of the
disclosure, a ratio of flowrates or partial pressures of the
precursors can be selected to promote high-quality film formation
under high volume manufacturing conditions.
In accordance with additional embodiments of the disclosure, a
structure includes one or more Si.sub.xGe.sub.1-xSn.sub.y
films--e.g., formed using a method disclosed herein. Structures can
also include additional layers, such as layers typically used to
form devices. For example, the structures can include a germanium
layer, which can form a buffer layer, and/or a fin layer as part of
a FinFET device.
In accordance with yet additional exemplary embodiments of the
disclosure, a device includes or is formed using a structure
including one or more Si.sub.xGe.sub.1-xSn.sub.y films.
And, in accordance with yet additional exemplary embodiments of the
disclosure, a system for forming one or more
Si.sub.xGe.sub.1-xSn.sub.y films includes a gas-phase reactor
including a reaction space, a germanium precursor (e.g., germane)
source coupled to the reaction chamber, a tin precursor source
coupled to the reaction space, and a silicon precursor (e.g.,
silane) source coupled to the reaction space. The system can be
configured to mix (e.g., have an operational control mechanism
configured to cause mixing of) one or more of the precursors (e.g.,
all precursors) at or near an inlet of a reaction chamber (e.g., at
an injection manifold).
Both the foregoing summary and the following detailed description
are exemplary and explanatory only and are not restrictive of the
present disclosure.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
A more complete understanding of exemplary embodiments of the
present disclosure may be derived by referring to the detailed
description and claims when considered in connection with the
following illustrative figures.
FIG. 1 illustrates a system for forming one or more
Si.sub.xGe.sub.1-xSn.sub.y films in accordance with exemplary
embodiments of the disclosure.
FIG. 2 illustrates a method of forming a Si.sub.xGe.sub.1-xSn.sub.y
film in accordance with further exemplary embodiments of the
disclosure.
FIG. 3 illustrates an XRD plot showing Si.sub.xGe.sub.1-xSn.sub.y
layers of various compositions grown with fixed SiH.sub.4,
GeH.sub.4, and SnCl.sub.4 flows formed in accordance with exemplary
embodiments of the disclosure.
FIG. 4 illustrates an RBS plot showing an exemplary
Si.sub.xGe.sub.1-xSn.sub.y layer on Ge buffer with 5% Sn and 8% Si
formed in accordance with exemplary embodiments of the
disclosure.
FIG. 5 illustrates Raman spectra of various
Si.sub.xGe.sub.1-xSn.sub.y films formed in accordance with
exemplary embodiments of the disclosure.
FIGS. 6-13 illustrate exemplary structures according to yet
additional exemplary embodiments of the present disclosure.
It will be appreciated that elements in the figures are illustrated
for simplicity and clarity and have not necessarily been drawn to
scale. For example, the dimensions of some of the elements in the
figures may be exaggerated relative to other elements to help to
improve understanding of illustrated embodiments of the present
disclosure.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE DISCLOSURE
The description of exemplary embodiments of methods, systems,
structures, and devices provided below is merely exemplary and is
intended for purposes of illustration only; the following
description is not intended to limit the scope of the disclosure or
the claims. Moreover, recitation of multiple embodiments having
stated features is not intended to exclude other embodiments having
additional features or other embodiments incorporating different
combinations of the stated features.
The present disclosure relates, generally, to methods of forming
layers, such as crystalline alloy layers including silicon,
germanium, and tin, overlying a substrate. The silicon germanium
tin (Si.sub.xGe.sub.1-xSn.sub.y) layers can include additional
elements, such as carbon, which forms part of a crystalline lattice
with the silicon germanium tin layer and/or dopants (e.g., p-type
dopants, such as boron (B) and/or n-type dopants, such as
phosphorous (P) and Arsenic (As)).
Exemplary Si.sub.xGe.sub.1-xSn.sub.y layers include from 0 or
greater than 0 at % to about 15 at % tin, about 2 at % to about 15
at % tin, or about 3 at % to about 12 at % tin.
Si.sub.xGe.sub.1-xSn.sub.y can include greater than 0 at % tin,
greater than 2 at % tin, or greater than 3 at % tin. The
Si.sub.xGe.sub.1-xSn.sub.y layers can additionally or alternatively
include from 0 or greater than 0 at % to about 30 at % silicon, or
about 1 at % to about 30 at % silicon, or about 3 at % to about 25
at % silicon. Exemplary Si.sub.xGe.sub.1-xSn.sub.y layers can
additionally or alternatively include about 55 at % to about 65 at
% germanium, or about 60 at % to about 70 at % germanium, or about
80 at % to about 90 at % germanium. When the layers include carbon,
the Si.sub.xGe.sub.1-xSn.sub.yC layers can include from 0 or
greater than 0 at % to about 1 at % carbon, or about 2 at % to
about 3 at % carbon, or about 4 at % to about 5 at % carbon.
The Si.sub.xGe.sub.1-xSn.sub.y layers can be used to form
structures and devices suitable for a variety of applications,
including strain layers to increase mobility of carriers in other
layers in semiconductor devices, as part of quantum well structures
and devices, and/or as layers in photonic devices. Exemplary
structures and devices are discussed below.
As used herein, a "substrate" refers to any material having a
surface onto which material can be deposited. A substrate can
include a bulk material such as silicon (e.g., single crystal
silicon, single crystal germanium, or other semiconductor wafer) or
can include one or more layers overlying the bulk material.
Further, the substrate can include various topologies, such as
trenches, vias, lines, and the like formed within or on at least a
portion of a layer of the substrate. Exemplary substrates include a
silicon wafer, a layer comprising germanium overlying silicon, and
a layer comprising germanium tin overlying silicon.
Turning now to the figures, FIG. 1 illustrates a system 100
suitable for forming Si.sub.xGe.sub.1-xSn.sub.y layers on a
substrate using the methods described herein. In the illustrated
example, system 100 includes a reactor 102, a silane source 104, a
germanium (e.g., germane) precursor 106 source, a tin precursor
source 108, purge and/or carrier gas source 110, an optional mixer
112, an optional intake plenum 114, and an exhaust (e.g., vacuum)
source 116. Sources 104-110 may be coupled to mixer 112 or reactor
102 using lines 118-132 and valves 134-140. Although not
illustrated, a system, such as system 100, may include additional
sources and corresponding delivery lines for other precursors, such
as carbon precursors and/or dopants (e.g., n-type dopants such as
phosphorous or arsenic or p-type dopants such as boron).
Additionally or alternatively, one or more dopants may be included
in one or more of the precursor sources 102-108. Further, although
separately illustrated, two or more dopants may be mixed in a
common source.
The sources can be relatively pure--e.g., about 99.999% or greater
pure or can be mixed with a carrier. In the case of silane, silane
source 104 can include about 1 to 10 at % silane in a carrier or
about 100 at % silane. Similarly, the germanium precursor source
106 (e.g., germane) can include about 1.5% to about 5 at % or about
10 at % germane in a carrier. Further, exemplary systems can
comprise, consist essentially of, or consist of the precursors
noted herein.
Reactor 102 can be a standalone reactor or part of a cluster tool.
Further, reactor 102 can be dedicated to a particular process, such
as a deposition process, or reactor 102 may be used for other
processes--e.g., for layer passivation, cleaning, and/or etch
processing. For example, reactor 102 can include a reactor
typically used for epitaxial chemical vapor deposition (CVD)
processing, such as an Epsilon.RTM. 2000 Plus, Epsilon.RTM. 3200,
or Intrepid XP, available from ASM, and may include direct plasma,
and/or remote plasma apparatus (not illustrated) and/or various
heating systems, such as radiant, inductive, and/or resistive
heating systems (also not illustrated). Using a plasma may enhance
the reactivity of one or more precursors. The illustrated reactor
is a single-substrate, horizontal-flow (cross-flow) reactor, which
enables laminar flow of reactants over a substrate 142, with low
residence times, which, in turn, facilitates relatively rapid
sequential substrate processing. An exemplary CVD reactor suitable
for system 100 is described in U.S. Pat. No. 7,476,627, issued to
Pomarede et al. on Jan. 13, 2009, the contents of which are hereby
incorporated herein by reference, to the extent such contents do
not conflict with the present disclosure. The cross-flow reactor
was found to produce high-quality Si.sub.xGe.sub.1-xSn.sub.y layers
on a surface of a substrate under conditions that are suitable for
high-volume, relatively low-cost manufacturing.
An operating pressure of a reaction chamber 144 of reactor 102 may
vary in accordance with various factors. Reactor 102 may be
configured to operate at near atmospheric pressure or at lower
pressures, which allows relatively fast formation of the
Si.sub.xGe.sub.1-xSn.sub.y layers--e.g., compared to ultra-high
vacuum or molecular beam epitaxy techniques. By way of examples, an
operating pressure of reactor 102 during layer formation steps
ranges from about 500 Torr to about 760 Torr, about 600 Torr to
about 760 Torr, or about 700 Torr to about 760 Torr. A reaction
space temperature can range from about 200.degree. C. to about
500.degree. C., about 275.degree. C. to about 475.degree. C., or
about 300.degree. C. to about 420.degree. C.
Silane source 104 includes silane (SiH.sub.4) and can optionally
include a carrier. Silane source 104 can optionally include one or
more dopant compounds, such as compounds typically used to
fabricate photonic and/or semiconductor devices. Exemplary p-type
dopant compounds include B.sub.2H.sub.6 and exemplary n-type dopant
compounds include PH.sub.3 and AsH.sub.3. Use of silane is
advantageous over the use of higher order silane compounds, such as
disilane, trisilane, tetrasilane (Si.sub.4H.sub.10), neopentasilane
(Si.sub.5H.sub.12), and higher order silanes, because silane is
relatively less expensive and is more readily available. The
inventors found that using pressures, a cross-flow reactor, and/or
the ratio of reactants disclosed herein allows for formation of
high-quality Si.sub.xGe.sub.1-xSn.sub.y layers using silane--rather
than higher order silanes.
Germanium precursor source 106 can include germane (GeH.sub.4) and
may optionally include one or more carrier gasses and/or dopant
compounds, such as compounds typically used to fabricate photonic
and/or semiconductor devices--e.g., B.sub.2H.sub.6 and/or PH.sub.3,
AsH.sub.3.
Use of germane is advantageous over other precursors, such as
digermane, trigermane, and other higher-order germanes, used to
form Si.sub.xGe.sub.1-xSn.sub.y layers, because germane is
relatively selective when mixed with various carrier gasses (e.g.,
hydrogen, nitrogen, or the like) and is also relatively selective,
even when dopants (e.g., p-type dopants) are used with the
precursor. Also, germane is relatively safe, compared to higher
order digermanes, and thus can be used and/or transported in higher
quantities, compared to higher order germanes. Also, germane can be
used as a precursor for other layers, such as germanium, and is
more readily available and is less expensive, compared to
higher-order germane compounds.
Tin precursor source 108 includes any compound suitable for
providing tin to a Si.sub.xGe.sub.1-xSn.sub.y layer. Exemplary tin
precursors include tin chloride (SnCl.sub.4), deuterated stannane
(SnD.sub.4), and methyl and/or halide substituted stannanes, such
as compounds having a formula Sn(CH.sub.3).sub.4-nX.sub.n, in which
X is H, D (deuterium), Cl, or Br and n is 0, 1, 2, or 3;
ZSn(CH.sub.3).sub.3-nX.sub.n, in which Z is H or D, X is Cl or Br,
and n is 0, 1, or 2; Z2Sn(CH.sub.3).sub.2-nX.sub.n in which Z is H
or D, X is Cl or Br, and n is 0 or 1; or SnBr.sub.4. Some exemplary
tin precursors suitable for use with the present disclosure are
discussed in more detail in application Ser. No. 13/783,762, filed
Mar. 4, 2013, entitled TIN PRECURSORS FOR VAPOR DEPOSITION AND
DEPOSITION PROCESSES, the contents of which are hereby incorporated
herein by reference, to the extent such contents do not conflict
with the present disclosure.
Purge and/or carrier gas source 110 may include any suitable purge
or carrier gas. Exemplary gasses suitable as carrier and purge
gasses include nitrogen, argon, helium, and hydrogen.
System 100 can also include a gas distribution system. An exemplary
gas distribution system, which allows for fast switching between
gasses (e.g., from sources 104-110) is set forth in U.S. Pat. No.
8,152,922 to Schmidt et al., issued Apr. 10, 2012, entitled "Gas
Mixer and Manifold Assembly for ALD Reactor," the contents of which
are hereby incorporated herein by reference, to the extent the
contents do not conflict with the present disclosure. The gas
distribution system may be used to, for example, mix one or more
precursor gasses and a carrier gas (which may be the same or
different from a purge gas from gas source 108) prior to the gasses
reaching plenum 114 or reactor 102.
Turning now to FIG. 2, an exemplary method 200 of forming a
Si.sub.xGe.sub.1-xSn.sub.y layer is illustrated. Method 200
includes the steps of providing a gas-phase reactor (step 202),
providing a substrate within the gas-phase reactor (step 204),
providing precursors to a reaction space of the reactor (step 206),
and forming a Si.sub.xGe.sub.1-xSn.sub.y layer overlying the
substrate (step 208). Method 200 can optionally include one or more
of forming an insulating layer overlying the substrate (step 210),
and/or forming a via within the insulating layer (step 212).
During step 202, a gas-phase reactor, such as a CVD reactor
suitable for epitaxial growth, is provided. The reactor can be a
single-substrate, laminar cross-flow reactor. Suitable reactors are
available from ASM, under the name Epsilon.RTM. 2000 Plus,
Epsilon.RTM. 3200, and Intrepid XP.
During step 204, a substrate is provided within a reaction chamber
of a reactor. The substrate may be received from a loading load
lock of a reactor system and transported to the reaction space,
such as a reaction chamber, using a suitable transfer mechanism.
During this step, the reaction space can be brought to a suitable
pressure and temperature for Si.sub.xGe.sub.1-xSn.sub.y layer
formation, such as the pressures and temperatures noted herein.
At step 206, the silane, germanium precursor, and the tin precursor
are provided to the reaction space of the reactor. The precursors
can comprise, consist essentially of, or consist of these
precursors. The silane, germanium precursor, and tin precursor can
be mixed (e.g., at mixer 112) prior to entering the chamber. The
silane, germanium precursor, and tin precursor can individually or
in various combinations be mixed with one or more carrier gasses
prior to entering the reaction space. One or more of the
precursors, in any combination, can be mixed with a carrier
upstream of the reaction chamber, such as at a mixer, upstream of a
mixer, and/or within the respective source. During this step, a
partial pressure of silane can range from about 5 Torr to about 20
Torr; a partial pressure of the germanium precursor (e.g., germane)
can range from about 300 Torr to about 450 Torr; or a partial
pressure of the tin precursor (e.g., tin chloride) can range from
about 1 Torr to about 3 Torr.
During step 208, a crystalline layer (e.g., an epitaxial layer) of
Si.sub.xGe.sub.1-xSn.sub.y is formed overlying a substrate. As
noted above, an operating pressure of a reaction space during layer
formation steps can range from about 500 Torr to about 760 Torr,
about 600 Torr to about 760 Torr, or about 700 Torr to about 760
Torr. And, a reaction space temperature can range from about
200.degree. C. to about 500.degree. C., about 275.degree. C. to
about 475.degree. C., or about 300.degree. C. to about 420.degree.
C.
During step 210, any suitable insulating layer, such as silicon
oxide or silicon nitride, is deposited onto the substrate. Then,
during step 212, one or more vias are formed within the insulating
layer. Reactive ion etching or other suitable technique can be used
to form the one or more vias.
In the cases where steps 210 and 212 are performed, the
Si.sub.xGe.sub.1-xSn.sub.y layer formed during step 206 can be
selectively formed within the vias. As noted above, use of a
germane precursor is advantageous because it is relatively
selective when using a variety of carrier gasses, such as hydrogen,
and/or when the layer includes one or more dopants, such as p-type
dopants.
FIG. 3 illustrates an X-Ray diffraction (XRD) plot of
Si.sub.xGe.sub.1-xSn.sub.y layers of various compositions grown
with fixed silane, germane, and tin chloride flow rates over a
layer of germanium overlying a silicon substrate. A reaction space
temperature during the deposition of the films varied between
300.degree. C. and 375.degree. C. The plot illustrates that a
composition of the Si.sub.xGe.sub.1-xSn.sub.y layers can be
adjusted to be lattice matched to germanium or can be increasingly
strained.
FIG. 4 illustrates aligned and random yield of Rutherford
backscattering spectra of a Si.sub.xGe.sub.1-xSn.sub.y layer formed
overlying a germanium layer on a silicon substrate. The
Si.sub.xGe.sub.1-xSn.sub.y includes about 5% tin and about 8%
silicon and was grown at a temperature of about 320.degree. C. The
low yield of the aligned spectra relative to the random spectra
indicates that the Si.sub.xGe.sub.1-xSn.sub.y layer is a
substitutional alloy.
FIG. 5 illustrates Raman spectra of Si.sub.xGe.sub.1-xSn.sub.y
layers of various compositions, illustrating ternary binding in the
films and that the films are substitutional alloys.
FIGS. 6-12 illustrate exemplary structures 600-1200 that can be
formed--e.g., using the exemplary systems and/or methods described
herein.
Structure 600 includes a substrate 602, a buffer layer 604, and a
Si.sub.xGe.sub.1-xSn.sub.y layer 606 (e.g., epitaxially formed
overlying layer 604). Substrate 602 can include, for example, a
silicon substrate. Substrate 602 can include additional layers of
materials used to form electronic or photonic devices. Buffer layer
604 can include or be, for example, a layer of germanium that is
epitaxially formed overlying substrate 602.
Si.sub.xGe.sub.1-xSn.sub.y layer 606 can be formed using, for
example, method 200. Structure 600 can be used to form a variety of
electronic or photonic devices.
A thickness of buffer layer 604 can range from, for example, about
0.5 to about 0.7, or about 0.8 to about 0.9, or be about one micron
thick. A thickness of Si.sub.xGe.sub.1-xSn.sub.y layer 606 can
range from about 1 to about 9, or about 10 nm to about 100 nm in
thickness.
Structure 700 is similar to structure 600, except structure 700
includes an additional layer 708. Structure 700 includes a
substrate 702, a buffer layer 704, a Si.sub.xGe.sub.1-xSn.sub.y
layer 706, and a germanium layer 708. Substrate 702, buffer layer
704, and Si.sub.xGe.sub.1-xSn.sub.y layer 706 can be the same as
the corresponding substrate and layers described in connection with
FIG. 6 and can have the same thicknesses. A thickness of germanium
layer 708 can range from about 1 to about 3, or about 4 to about 9
or be about 10 nm thick. Germanium layer 708 can be epitaxially
formed overlying Si.sub.xGe.sub.1-xSn.sub.y layer 706 using, e.g.,
an epitaxial process with germane as a precursor.
Structure 800 includes a substrate 802, a buffer layer 804, a
Si.sub.xGe.sub.1-xSn.sub.y layer 806, and a germanium tin (GeSn)
layer 808 epitaxially formed overlying Si.sub.xGe.sub.1-xSn.sub.y
layer 806. Substrate 802 and layers 804-806 can be the same or
similar to corresponding layers described above in connection with
FIGS. 6 and 7 and have the same thicknesses. GeSn layer 808 can
have a thickness of about 1 to about 3, or about 4 to about 9, or
be about 10 nm. GeSn layer 808 can be formed by, for example, using
germane and a tin precursor such as tin chloride. GeSn layer 808
can include, for example, about 1 at % to about 8 at % or about 9
at % to about 15 at % tin.
Structure 900 includes a substrate 902, a germanium layer 904, a
GeSn layer 906, and a Si.sub.xGe.sub.1-xSn.sub.y layer 908. The
composition of the layers can be the same as the corresponding
layers described above in connection with FIG. 8 (with germanium
layer 904 corresponding to buffer layer 804). In the illustrated
example, buffer layer 904 can have the same thickness as buffer
layers 604-804; a thickness of GeSn layer can range from about 100
nm to about 400 nm, or about 500 nm to about 900 nm, or be about
1000 nm. Si.sub.xGe.sub.1-xSn.sub.y layer 908 can have the same
thickness as Si.sub.xGe.sub.1-xSn.sub.y layers 606, 706, and 806.
Structure 900 is similar to structure 800, except GeSn layer 906
and Si.sub.xGe.sub.1-xSn.sub.y layer 908 are formed in reverse
order--compared to the structure illustrated in FIG. 8.
Structure 1000, which is suitable for quantum well structures and
devices, includes a substrate 1002, a buffer layer 1004, first
Si.sub.xGe.sub.1-xSn.sub.y layer 1006, GeSn layer 1008, and second
Si.sub.xGe.sub.1-xSn.sub.y layer 1006. The various layers can be
formed as described above. Buffer layer 1004, first and second
Si.sub.xGe.sub.1-xSn.sub.y layers 1006 and 1010, and GeSn layer
1008 can have the same thickness noted above. By way of example,
buffer layer 1004 can be about 1 micron thick, first
Si.sub.xGe.sub.1-xSn.sub.y layer 1006 and second
Si.sub.xGe.sub.1-xSn.sub.y layer 1010 can each be about 50 nm
thick, and GeSn layer 1008 can be about 10 nm thick. Layers
1008-1010 can be repeated a desired number of times to form a
quantum well structure.
FIG. 11 illustrates another structure 1100 that is suitable for use
as a quantum well structure or device. Structure 1100 includes a
substrate 1102, a buffer layer 1104, a first
Si.sub.xGe.sub.1-xSn.sub.y layer 1106, a first Ge layer 1108, a
GeSn layer 1110, a second Ge layer 1112, and a second
Si.sub.xGe.sub.1-xSn.sub.y layer 1114. Buffer layer 1104, first and
second Si.sub.xGe.sub.1-xSn.sub.y layers 1106 and 1114, first and
second Ge layers 1108 and 1112, and GeSn layer 1110 can have the
same thickness noted above. By way of example, buffer layer 1104
can be about 1 micron thick, first Si.sub.xGe.sub.1-xSn.sub.y layer
1106 can be about 50 nm thick, first Ge layer 1108 and second Ge
layer 1112 can be about 50 nm thick, GeSn layer 1110 can be about
10 nm thick, and second Si.sub.xGe.sub.1-xSn.sub.y layer 1114 can
be about 10 nm thick. Layers 1106-1114 can be repeated a desired
number of times to form a quantum well structure.
FIG. 12 illustrates yet another structure 1200 in accordance with
various embodiments of the disclosure. Structure 1200 includes
substrate 1202, first Si.sub.xGe.sub.1-xSn.sub.y layer 1204, GeSn
layer 1206, and second Si.sub.xGe.sub.1-xSn.sub.y layer 1208.
Structure 1200 is similar to structure 1000, except structure 1200
does not include buffer layer 1004. The layers of structure 1200
can be formed using the same techniques used to form structure 1000
and the layers can have the same or similar thicknesses.
FIG. 13 illustrates yet another structure 1300 in accordance with
additional exemplary embodiments of the disclosure. Structure 1300
includes a substrate 1302, an insulating layer 1304, a via 1306
formed within insulating layer 1304, a germanium layer 1308 (e.g.,
epitaxially formed overlying substrate 1302), and a
Si.sub.xGe.sub.1-xSn.sub.y layer 1310 (e.g., epitaxially formed
overlying layer 1308). Layers 1308 and/or 1310 can be selectively
formed within via 1306--e.g., using method 200. Substrate 1302,
germanium layer 1308, and Si.sub.xGe.sub.1-xSn.sub.y layer 1310 can
be the same or similar to respective layers described above and can
have the same or similar thicknesses. Insulating layer 1304 can
include silicon oxide, silicon nitride, and/or silicon oxynitride.
A thickness of insulating layer 1304 can range from about 1 to
about 10 nm, or about 10 to about 100 nm.
It is to be understood that the configurations and/or approaches
described herein are exemplary in nature, and that these specific
embodiments or examples are not to be considered in a limiting
sense. In the case of exemplary methods, specific routines or steps
described herein can represent one or more of any number of
processing strategies. Thus, the various acts illustrated can be
performed in the sequence illustrated, performed in other
sequences, performed simultaneously, or omitted in some cases.
The subject matter of the present disclosure includes all novel and
nonobvious combinations and subcombinations of the various
processes, layers, systems and configurations, and other features,
functions, acts, and/or properties disclosed herein, as well as any
and all equivalents thereof.
* * * * *